Conventionally, a resilient bush that is used to support a suspension arm typically comprises an inner sleeve, a resilient body fixed to the circumference of this inner sleeve, and an outer sleeve fixed to the circumference of the resilient body; fixing is effected by pressure-insertion of the outer sleeve into a support hole formed in the suspension arm; however, with this bush, metallic members constituted by the suspension arm and outer sleeve are fitted together by insertion, so precise processing of the inside face of the support hole of the suspension arm is required, increasing processing costs, and making it necessary to use a high pressure-insertion load, which increases the equipment cost of the pressure-insertion device; in addition, the unit cost of the bush itself is raised by the provision of the outer sleeve, making it difficult to achieve reduction in costs.
Resilient bushes are also conventionally known of the outer-sleeveless type, wherein the resilient body is made to directly contact the inside face of the support hole of the suspension arm, dispensing with the outer sleeve. With these bushes, the processing precision of the inside face of the support hole need only be rough and the pressure-insertion load can be low, so equipment costs are lowered and, in addition, the unit cost of the bush itself is lowered, making possible considerable cost savings.
In both resilient bushes of the outer sleeveless type and the type fitted with an outer sleeve, resilient bushes are known, wherein an inserted sleeve is embedded in a diametrically intermediate region of the resilient body, in order to raise the spring constant of the resilient bush in the diametrical direction.
Although resilient bushes of the outer sleeveless type referred to above have the advantage of enabling cost savings to be achieved as described above, they have the severe drawback that, since fixing to the article to be supported such as the suspension arm is obtained solely by the degree of tightening of the resilient body that can be achieved, the withdrawal load that they can withstand is greatly lowered compared with bushes of the type fitted with an outer sleeve, hence they cannot be employed in locations where they are subjected to load in the withdrawing direction or where they are subjected to complex inputs. Also, because of considerations regarding ease of pressure-insertion and shape stability after insertion (protrusion of the resilient body etc), the volume of the resilient body of the bush must be restricted, but, as a result, the initial compression ratio of the resilient body is limited so, even though an inserted sleeve is embedded in the resilient body, it is inferior in regard to spring balance performance in the diametrical direction, axial direction and torsional direction compared with a bush of the type fitted with an outer sleeve.
In view of the above, an object of the present invention is to provide a resilient bush of the outer sleeveless type, wherein the withdrawal load is large and, furthermore, performance can also be improved.